Off-Grid Grid-Down Comms & Current consumption

Stop telling people to turn down the TX power on their QRO ham radio for more efficient comms. It’s complete bull-hockey!

Hello Operators.
Just a short rant giving the community the real dope on operating a fixed or field, solar-powered ham radio station more efficiently, in an off-grid or grid-down scenario.

There’s a reason I use portable radios at home and in the field. The reason is current consumption. QRP rigs are much more efficient than any QRO radio currently on the market. If you’re planning to use ham radio equipment for off-grid or grid down communications where you must generate your own power, a Yaesu 991A, Icom IC-7300, Yaesu FT857, FT-891, or any radios designed for use at home or in a vehicle are A COMPLETE NO-GO! QRO rigs are ridiculously inefficient. 1-3 amp RX current draw, 18-24 amps current draw at 100 watts TX. This is not sustainable without massive energy generation and battery storage. Building the energy generation and battery storage will be unnecessarily expensive, for that current hungry QRO radio. Moreover, you’ll still have an inefficient station. I’ll explain.

There are “those” people saying “just turn the power down and its the same as a QRP radio”. No! These are the words of an idiot!

Turning your TX power down on a QRO rig does not:

  • increase efficiency on TX. It will reduce power at the cost of signal strength, but the inefficient final stage continues wasting energy.
  • reduce RX current draw. The average current consumption on popular HF and VHF/UHF mobile rigs is ~2 amps.

In contrast, the “worst” QRP radio in terms of current consumption was perhaps the FT-817/FT-818. It’s TX current draw was fine, but the RX current consumption is what should be considered as “the top end” of what we want. For example, The Icom IC-705 and Lab599 TX-500, Elecraft KXx, trUSDX, FX-4CR, … all have extremely good RX current consumption. The Xiegu G90 is there as an example of what is “good enough”.

For the sake of our discussions, any rig with RX current under an 900ma is not great, but can be made to work in regions and latitudes with lots of sun. Any rig with RX current under 500ma is sustainable in most regions and latitudes in all but winter months. 500ma rigs can even be looked at as “the goal post”. Any rig with 300ma or less is EXCELLENT!

The reason we reach for such low current consumption is it reduces the battery capacity and solar panel requirements. Imagine the difference in run time with a 10ah battery if our radio is constantly putting a 1 amp load on our battery. Now imagine the runtime with that same battery if it is only putting a 300ma load on it. Naturally, we get much longer operating time with lower RX current. This means we could reduce the size of the battery and solar panel if using one, without diminishing our operating time.We will appreciate this weight reduction the next time our stations must be carried on our backs.

Yaesu FT-891: Great Example

On a trip to Lapland a few years ago, I carried and deployed the Yaesu FT-891 man-portable. Although I was able to generate enough power to cover the RX current, I wasn’t able to generate enough energy to maintain effective communications! As long as the station was primarily receiving, things were ok. The TX side was the Achilles heal in that scenario. At 100 watts, the rig was putting a nearly 20 amp load on my 10ah battery. There was no man-portable way to reconcile that TX current consumption shortfall with my solar panels at 66 North. The rain, clouds and overcast made it too difficult to replenish the battery. So I could either charge the battery with the radio off, or receive signals, but not recharge the battery. Perhaps it would have worked in the sand dunes of Arizona or New Mexico, but not in New England, PNW, Northern Europe or Scandinavia. On that trip, the FT-891 was just short of being a boat anchor.

This was an important expedition in regards to current consumption, but most haven’t paid any attention to it.

My solution

Ultimately I figured out the RX current consumption and TX efficiency of QRP radios was superior to all the QRO radios on offer. I ultimately purchased QRP rigs and amplifiers to get more efficiency and higher power output from the setup. This is not the most cost-effective solution, but it is the ultimate way to achieving the lowest current-hungry communications gear available. Of course having a QRO all-in-one station like a modernized Yaesu FT-897D with internal DIY LiFePO4 battery bay, low RX current draw and 20-watts output would be ideal, but that radio doesn’t exist.

My Icom IC-705 and PA500E expedition amplifier are putting an RX load of less than 300ma on my battery (combined). Moreover, the IC-705 and PA500E combo package put out a 100-watt signal, using less than 12 amps of current. There are no QRO rigs available today that can achieve this level of efficiency. In fact, manufacturers don’t even consider “efficiency” as a requirement in desktop and mobile radios. I fear they will find how wrong that assumption is, as the price per Kw of grid-tied electricity transitions from being calculated in $$ USD, and begins being calculated in kidneys and children.

Although I still operate quite low power, both my fixed station and field station can put out 100 watts if need be. That’s 100 watts with a 12 amp load on TX, and less than 300ma on RX. This is sustainable current consumption! Every piece of radio gear I choose must comply with this low current consumption methodology. The computers, the radios, the lights, everything. Ultimately, this will reduce the load when man-portable, and make us more efficient & effective whether operating fixed or field stations.

Even if we only plan on operating fixed station from home, there is much to be learned from the off-grid ham radio Operator. The lesson of efficiency is one we should all be taking seriously in preparedness. Anyone promoting a high-current radio for off-grid or grid-down survival communications is delusional. It isn’t sustainable, and won’t work in the long-term.

Off-Grid Ham Shack on solar power

Solar power for portable ham radio

Julian oh8stn
Off-Grid Ham Radio blog:

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  1. I have installed and used multiple solar systems on home, and our RV which currently has 2400w of solar installed on it.

    I talk with people that think they can install 600w of solar on their roof, and run their homes central system on it without batteries that are hams, so I feel your fustration.

    My daughters 12 and 15 have both a 705 and a 7300, and as much as we could do the math and talk about these things, they really learned when I made them get the electrons back from a 114AH lead acid cell, after using their 7300 one night.

    I had them make and solder all the jumper cables, install the MC connectors, and they then got to haul the heavy batter to the field near us, then setup the solar system, and stand their for 3 hours tilting the panels into the sun, playing the human 2 legged tracker game.

    While not the nicest thing to do, yes they could have made a small rack out of something, it sure gave them the real wold experience of seeing how just a slight wrong angle, or just a little shade on a panel effected the rate of charge.

    Thats real world experince, and I wish more people actually had some.


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